Harvested vegetables are alive and why MAP and EMAP is the key to keep vegetables, fruits and salad fresh
Indeed, vegetables still live once they’re harvested. In other words they still breath or respire. Fortunately, I have found a good article about their respiration.
This article explains why respiration is essential for vegetables to continue living. And for keeping produce good it is important they stay alive. Once respiration stops, decay will set in very quickly.
The trick to storing vegetables, salads and fruits for a long period of time is thus to keep respiration going for as long as possible. This can be done by slowing down respiration as much as possible (without stopping it).
This is why EMAP is vital for keeping vegetables, salads and fruits in both whole products and cutted products, fresh in the longest possible time. EMAP or Equalibrium Modified Atmosphere Packaging brings the packaging in balance with the packed product. EMAP Packaging is perforated with tiny small holes, typically from 70 to 120 micron. This is the same size as the diameter of a human hair!!! Just one hole of this size can totally change your packaging from a packaging the helps and extends the shelf life of our product, to a packaging that actually reduces the shelf life of your product.
The key is the knowledge of measuring respiration and calculating permeability and of course some knowledge of the product you pack in the packaging.
Optimizing oxygen & carbon dioxide contents
One way to slow own respiration is by controlling the levels of oxygen and carbon dioxide.
For some products like iceberg and romaine, the ideal oxygen level is very low. Typically below 1% O2,.If you have an higher level of O2 you will risk that the white parts of the product changes its color to pink. A higher level of O2 will also increase bowning on the cuttet surfaces.
For other products like rocket salad, spinage and other types of babyleaf, it is bennificial to have a level of O2 arround 10 - 15 %, With this level of O2 you might not get the longest possible shelf-life, but if you expose theese products to lower levels of O2, the consumer who opens the packaging will have a negative experience due to off odors (bed smell).
The reduced oxygen concentration will slow down the respiration rate, which will again extend the shelf life of the packed product
Carbon dioxide unfortunately, is a slightly more complex story. Vegetables differ a lot in how they react to carbon dioxide. Though, generally saying you should increase carbon dioxide content around vegetables to decrease respiration rate.
This is indeed opposite of what should be done with oxygen. However, whereas oxygen is consumed during respiration, carbon dioxide is produced during respiration. This explains the difference.
The difference between MAP and EMAP
MAP is an abbreviation of Modified Atmosphere Packaging. MAP is typically made with a packaging film with barrier properties (like mono PET or laminates with sealing layers and/or different film layers with barrier properties). MAP films typically have a low OTR (Oxygen Transmission Rate) of < 100 ml/m2/24h/atm, the transmission rate of the film is also called permeability of the film. In the moment of packing the product into the packaging (typical a bag or a tray with a sealed lid) the packs are flushed with gas, which is typical N2 or a mix of gas types. When you flush with for example N2, the O2 around the product in the package will be removed (flushed away) and replaced with N2. N2 is in most cases is harmless for the product.
EMAP is an abbreviation of Equilibration Modified Atmosphere Packaging. EMAP is typically made with packaging film without barrier properties like OPP or PE. The packaging films for EMAP, typically has OTR values ranging from 1000 ml/m2/24h/atm and up to about 4000 ml/m2/24h/atm. Most vegetables, fruits and salads require OTR values between 7000 and up to 40.000 ml/m2/24h/atm for creating the best possible environment inside the packed packaging. Laser perforation is commonly used to modify the OTR of EMAP packing films. The holes made with laser typically has a size of 70 to 120 micron, this means that they are almost invisible for the human eye. The size of the laser hole and the number of holes per package determines the OTR for the package.
When to use MAP or EMAP
For products without respiration like meat, cheese etc. these products are all packed in MAP. This means that the level of O2 and CO2 can be 100 % controlled from the moment of packing and the level of O2 and CO2 stays the same through the lifetime of the product.
Products with respiration like vegetables, fruit and salads etc. will have great benefits of using an packaging film specially made for EMAP.
In the moment of packing the product is packed with the surrounding air (20,9 %O2 and 0,3 % CO2) due to the respiration the products with start to use the O2 in the package and produce CO2. As the level of O2 in the package decreases, air from the outside of the packaging will start to enter the packaging via the laser perforated holes. At the same time, due to the respiration the CO2 increases inside the package, so the CO2 will also flow through the laser perforated holes. After hours and days, the product and the EMAP package will enter a balance at its equilibrium. Depending on the respiration of the product and number and size of laser perforated holes, the equilibrium level can be controlled.
Use of EMAP in combination with gas flushing
The optimum conditions for prolonged shelf-life, is first met when the packed product reaches its equilibrium, depending on the product respiration this can have a duration of up to 24 hours or longer. In this time where the product is not kept under optimum O2 and CO2 conditions, the product reduces its shelf-life. Therefore, it is important that the product reaches its equilibrium as fast as possible.
The way to achieve this is with gas flushing. This means that the packed product, is at the optimum level of O2 and CO2 at the moment of packing. Because of the laser perforated holes, the level of O2 and CO2 will remain at the correct level, throughout the shelf-life of the product.
This can be seen as the ideal packing process for many types of vegetables, fruit and salads.